1. Field of the Invention
The present invention relates to a fuel vapor processing apparatus for processing fuel vapor that may be produced within a fuel tank.
2. Description of the Related Art
A known fuel vapor processing apparatus includes a tank-side adsorption material contained in a first space communicating with a space within a fuel tank, and an atmosphere-side adsorption material contained in a second space having one end communicating with the first space via a communication passage and having the other end open into the atmosphere. Therefore, the tank-side adsorption material within the first space can adsorb fuel vapor dissipated from the space within the fuel tank. The atmosphere-side adsorption material within the second space can adsorb a part of the fuel vapor that may be leaked from the first space.
This type of fuel vapor processing apparatus is disclosed, for example, in Japanese Laid-Open Patent Publication No. 10-37812. As shown in FIG. 9, a fuel vapor processing apparatus disclosed in this publication includes a first canister 101 and a second canister 102. The first canister 101 has a first space 101s defined therein and containing activated carbon C. The second canister 102 has a second space 102s defined therein and containing honeycomb activated carbon H. The first canister 101 includes a tank port 101t communicating with a space defined within a fuel tank (not shown), so that fuel vapor dissipated from the space within the fuel tank can be adsorbed within the first canister 101. The second canister 102 can adsorb a part of the fuel vapor leaked from the first canister 101 and is connected to the first canister 101 via a communication pipe 103. The second canister 102 is formed with an atmospheric port 102e at an end surface on the side opposite to the communication pipe 103.
Therefore, for example, during filling of fuel into the fuel tank, air within the fuel tank may be discharged to the atmosphere from the atmospheric port 102e via the first canister 101, the communication pipe 103 and the second canister 102.
According to the fuel vapor processing apparatus of the above publication, a part of the fuel vapor leaked from the first canister 101 may quickly reach the second canister 102, because the first canister 101 and the second canister 102 are connected to each other by the communication pipe 103 that has a relatively thin diameter. In other words, a fuel vapor dissipation preventing effect of the communication pipe 103 is small, and therefore, an amount of dissipation of the fuel vapor toward the side of the second canister 102 is large.
This can be improved by setting the length of the communication pipe 103 to be large. However, if the length of the communication pipe 103 is large, the resistance against flow of air within the communication pipe 103 increases to prevent smooth flow of air within the communication pipe 103 when air within the fuel tank is allowed to be released to the outside, for example, during filling of fuel into the fuel tank.
Therefore, there is a need in the art for a fuel vapor processing apparatus that can decrease the amount of dissipation of fuel vapor from a first space into a second space and can minimize resistance of flow of air when air flows between the first space and the second space.